How could new-build homes be improved to encourage more renewable energy use?

I believe we need to take bigger steps in creating a world that relies on renewable energy; and one way to take a step in the right direction is to build homes that have the ability to run on renewable energy. Many homes we live in now are decades if not centuries old, and therefore we should have the future in mind when building new homes. We are moving towards a renewable energy world, so why are we not building for it. One way which new homes could encourage renewable energy use, is to be fitted with solar panels. With more and more houses having solar panels fit to their roofs, why do we not start building homes with solar panels already there? Thus making it standard practice. I would suggest that a rule is put in place, for the UK anyway, for every new build home to be fitted with solar panels. The cost could be a factor against this, but surely having a solar panel in the home is a selling point in itself.